1. Field of the Invention
The present invention relates to an image recording apparatus for recording an image on a recording medium.
2. Related Background Art
In a conventional recording apparatus, such as an ink jet recording apparatus, a paper feeding means comprising a pair of rollers etc. is disposed in the upstream side of the platen with respect to a conveying direction in which a recording medium such as a recording paper or a clear sheet for OHP is supplied along the platen, while in the downstream side of the platen a paper discharge means comprising a pair of rollers etc. is disposed. Further, in the vicinity of the paper feeding means and the paper discharge means, a paper feeding sensor and a paper discharge sensor are provided, respectively, for detecting the presence of the recording medium. A recording head is mounted on a carriage reciprocally moving between the paper feeding means and the paper discharging means in the direction perpendicular to the conveying direction (hereinafter referred to as "paper width direction"), the recording head being opposed to the recording medium on the platen with a predetermined space therebetween. A paper width sensor is provided near a recording head of the carriage to read out a difference between a reflecting light amount from the platen and that from the recording medium to detect a width of the recording medium (hereinafter referred to as "paper width") and a kind of the recording medium (hereinafter referred to as "paper kind").
A method for controlling such an ink jet recording apparatus will now be described.
(1) Normal Mode
In this mode, firstly, the recording medium is fed by the paper feeding means along the platen by a paper feeding amount required to make the rear end of the recording medium reach the paper discharging means from a position detected by the paper feeding sensor disposed at the upstream side of the platen. At this time, the presence of the recording medium is detected by the paper discharging means disposed at the downstream side of the platen. If the detected result shows an absence of any recording medium, an indication is made to inform generation of jamming by judging that the recording medium does not reach the paper discharging means. If the paper discharging sensor detected that the recording medium is present, it is considered that the recording medium reaches the paper discharge means and then the carriage is moved to detect the paper width and the paper kind. Thereafter, the recording operation starts.
In this normal mode, a large blank area where nothing is recorded is generated due to the distance between the rear end of the recording medium and the position where the recording head records. Therefore, there has been proposed a leading and rear end mode in which the recording operation is started from a position immediately near the rear end of the recording medium, without producing a large blank.
(2) Leading and Rear End Mode
In this mode, firstly, the recording medium is fed toward the platen by the paper feeding means, and the paper feeding sensor judges whether the rear end of the recording medium has reached the paper feeding sensor. If the sensor detects no paper, the paper feeding operation continues. If paper is detected, the rear end of the recording medium is fed in the conveying direction along the platen by the paper feeding means by a predetermined paper feeding amount A required to make the rear end of the recording medium pass over the recording position of the recording head. Next, the carriage is moved in the paper width direction to detect the paper width and the paper kind by the paper width sensor, and the resulting signal pattern therefrom will be used to judge the paper kind. If the paper width sensor is judged as being abnormal, it is informed. Otherwise, a signal indicating that the paper is a predetermined recording paper or a clear sheet for OHP is output to judge the paper width, and thereafter, the recording operation starts.
In the method for controlling the ink jet recording apparatus described above, in the normal mode it is possible to judge by the paper discharging sensor if the recording medium is correctly supplied to the paper discharging means. But in the leading and rear end mode, even if the recording paper is correctly fed by a predetermined paper feeding amount, the rear end of the recording medium does not reach the paper discharging means, leading sometimes to a case in which it is not possible to judge by a sheet exhaust sensor or a paper discharging sensor if the recording medium is correctly fed.
Further, in either mode, in order to perform a successive recording operation, it is necessary to delicately adjust the rotating angle of the driving motor and the ink outlet opening at the time of stepping feeding in which the sheet member passes out from the conveying upper and lower rollers 7, 8, for increasing the interfacing accuracy particularly after completing the recording operation for one sheet for shifting to the next sheet. For this purpose, it is indispensable to accurately detect the remaining amount of the rear end of the sheet member from the conveying upper and lower rollers 7, 8.
Therefore, the number of stepped feedings of the sheet member by the conveying roller from the sheet member is detected as one of fixed sizes on the basis of the number of stepped feedings until the rear end of the sheet member passes trough the paper sensor, thereby judging the remaining amount of the rear end of the sheet member. This method, however, has the following disadvantage.
That is, there would arise cases where any optimum controlling operation in accordance with the remaining amount at the respective rear end of each sheet member becomes impossible. Such cases include one in which an indefinite sheet member passes through the paper sensor by accidentally the same number of stepped feedings as that for a definite size sheet member, and another case in which the paper sensor undesirably detects the rear end by the same number of times for the stepped feedings when the difference of length of sheet members between one of A5 size (148.times.210 mm) and 5.5.times.8.5 inches (139.7.times.215.9 mm), in this case, the difference being 5.9 mm, is less than the feeding amount for one step. As a result, it becomes impossible to perform the optimum controlling operation corresponding to the remaining amount of the rear end of the respective sheet member.
Further, in addition to the problem of the paper feeding accuracy, a disadvantage is that white lines between an image recorded at the first line and an image recorded at the second line due to the floating of the paper on the platen when the paper is conveyed.
Namely, although the paper is conveyed through the paper feeding rollers and the paper discharging rollers, the rear end of the paper would not smoothly enter into a pair of paper discharging rollers so as to float on the platen due to the rolling at the rear end of the paper when the rear end of the paper is supplied into the paper discharging rollers.